Summary Of Significant Accounting Policies (Schedule Of Calculation Of Basic And Diluted Earnings Per Share) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended												12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Earnings Per Share Reconciliation [Line Items]
Net income	$ 24,011	$ 17,156	$ 22,150	$ 19,125	$ 67,489	$ 23,726	$ 8,457	$ 11,487	$ 18,115	$ 19,314	$ 13,580	$ 5,598	$ 82,442	$ 111,159	$ 56,607
Denominator for basic earnings per share - weighted-average number of common shares outstanding during the period													53,538,000	54,213,000	56,320,000
Incremental common shares attributable to exercise of dilutive options													450,000	324,000	150,000
Incremental common shares attributable to outstanding restricted shares and restricted stock units													234,000	242,000	164,000
Denominator for diluted earnings per share													54,222,000	54,779,000	56,634,000
Basic earnings per share	$ 0.45	$ 0.32	$ 0.41	$ 0.36	$ 1.26	$ 0.44	$ 0.16	$ 0.21	$ 0.33	$ 0.35	$ 0.24	$ 0.10	$ 1.54	$ 2.05	$ 1.01
Diluted earnings per share	$ 0.45	$ 0.32	$ 0.41	$ 0.35	$ 1.24	$ 0.43	$ 0.16	$ 0.21	$ 0.33	$ 0.34	$ 0.24	$ 0.10	$ 1.52	$ 2.03	$ 1.00
Anti-dilutive options to purchase common shares													700,000	1,200,000	3,700,000